1. Field of the Invention
This invention relates to rheologically modified polyol compositions using reticulated bacterial cellulose as the rheological modifying agent.
2. Related Background Art
Rheologically modified, or viscosified, polyol compositions have many uses. They have been used for fluid retention/sealant systems such as tire sealants, fluid drives and the like. Polyols, and polyethylene glycols in particular, are frequently added in conjunction with other components for various applications in cosmetics, for example, molded sticks (lipstick), sunscreens, astringents, shaving products including pre-shave, shave gel and cream, and aftershave. Polyols are common additives in other personal care products, such as hair fixatives, colorants, and conditioners, and are frequently used as delivery vehicles for scalp treatments. In each of these applications, the combination of polyols with a rheological modifying agent forms viscosified compositions that provide products that are easy to use and apply.
Rheologically modified polyols provide enhanced flow and cling properties to various humectants, such as in toothpaste and gels. Synthetic lubricants represent yet another application wherein the enhanced rheology of polyol base fluids build cling and sag control and prevent flow off of the lubricant. Due to the ability of the Theologically modified polyols to suspend particulates, these viscous compositions may be used as fluid delivery compositions or carriers for certain materials. Metal working fluids containing such rheologically modified polyols may be used as an aid to transport cuttings. Additionally, these fluid compositions may be used as carriers or delivery vehicles for other particulate materials, e.g., water-soluble hydrocolloids. These delivery and surface cling features are important in other applications as well, such as in varnish and paint removers and other painting applications.
Rheologically modified polyols have been used in oil field operations, e.g., in drilling fluids, workover/completion fluids, cementing fluids, oil well insulating fluids, as ballast materials, non-petroleum based hydraulic fluids, and the like.
The conveyance of oil obtained from offshore fields requires specially designed systems. Sometimes, the temperature of oil, pumped from beneath the ocean floor, is about 104.degree.-121.degree. C. (220.degree.-250.degree. F.), yet the temperature of the water through which the oil must be conveyed can be as low as 0.degree.-10.degree. C. (32.degree.-50.degree. F.). Any system for conveying oil through such a low temperature environment must provide a suitable means for insulating the oil from the low temperature of the surrounding environment.
Failure to provide adequate insulation results in reduction of the oil temperature. It is important to maintain high oil temperature to retain low viscosity and high pumpability of the oil as it is pumped through the pipeline. As the temperature decreases, the viscosity of the oil increases making it more difficult to pump. Further, at lower temperatures, separation and crystallization of the various hydrocarbon fractions present in the oil may result. For example, paraffins, low viscosity hydrocarbons, medium viscosity hydrocarbons, oil sludge, and the like, may deposit on the pipeline walls gradually restricting oil flow. Thus, the means of conveyance, typically pipelines, must be insulated to achieve efficient flow of the oil.
Ramsay, et al., U.S. Pat. No. 5,290,768, describe the use of rheologically modified welan gum/ethylene glycol compositions as insulating fluids for oil pipelines. A chelating agent, such as ethylenediamine tetraacetic acid, is present in these compositions to minimize the deleterious effects of metal ion contaminants present in pipeline pumping operations. However, an improved rheologically modified composition which serves as a thermal insulating material having long term stability at high temperatures and in the presence of metal ion contaminants, without the necessity of added chelating agents, would be highly desirable for pipeline oil insulation.
Reticulated bacterial cellulose is a useful and unique rheological modifying, or viscosifying agent. Unlike water soluble viscosifying agents, such as various polysaccharide derivatives, guar gum, welan gum, xanthan gum or sodium alginate, reticulated bacterial cellulose is a colloidal network of ultra fine cellulose fibers. This network structure differentiates the reticulated bacterial cellulose used in this invention from other polysaccharide derivatives. When the ultra fine cellulose fibers of the reticulated bacterial cellulose are dispersed in a base fluid, the colloidal network expands throughout the fluid. In this dispersed form, the reticulated bacterial cellulose is insensitive to many of the harsh conditions that adversely impact soluble polysaccharide materials, such as harsh temperatures, pH, salinity and shear.
As used herein, the term "reticulated bacterial cellulose" refers to cellulose produced by microorganisms using aerobic culturing techniques and is characterized by a highly reticulated, branching interconnected network of fibers that are insoluble in water. Reticulated bacterial cellulose may be produced by the genus Acetobacter under agitated conditions and is available, under the registered trade name Cellulon.RTM., from the NutraSweet Kelco Company, a unit of the Monsanto Company, St. Louis, Mo.
The preparation of reticulated bacterial cellulose is well known. For example, U.S. Pat. No. 5,079,162 and U.S. Pat. No. 5,144,021, both of which are incorporated by reference herein, disclose a method and media for producing reticulated bacterial cellulose aerobically, under agitated culture conditions, using a bacterial strain of Acetobacter aceti var.xylinum. Use of agitated culture conditions results in sustained production, over an average of 70 hours, of at least 0.1 g/liter per hour of the desired cellulose. Wet cake reticulated cellulose, containing approximately 80-85% water, can be produced using the methods and conditions disclosed in the above-mentioned patents. Dry reticulated bacterial cellulose can be produced using drying techniques, such as spray-drying, drum-drying, tray-drying or freeze-drying, that are well known.
Acetobacter is characteristically a gram-negative, rod shaped bacterium 0.6-0.8 .mu.m by 1.0-4 .mu.m. It is a strictly aerobic organism; that is, metabolism is respiratory, never fermentative. This bacterium is further distinguished by the ability to produce multiple poly .beta.-1,4-glucan chains, chemically identical to microcrystalline cellulose. The microcellulose chains, or microfibrils, of reticulated bacterial cellulose are synthesized at the bacterial surface, at sites external to the cell membrane. These microfibrils generally have cross sectional dimensions of about 1.6 nm.times.5.8 nm. Due to the small particle diameter, the microfibrils have a surface area several orders of magnitude higher than normal wood cellulose. It is this extremely high surface area that is responsible for many of the unique functional properties (viscosity, yield stress, binding properties etc.) of reticulated bacterial cellulose.
Aqueous rheologically modified compositions containing reticulated bacterial cellulose compositions have been used in oil production applications. U.S. Pat. No. 5,009,797 discloses a high viscosity aqueous hydraulic fracturing fluid composed of an aqueous based mixture of reticulated bacterial cellulose and a gellant. Aqueous crosslinked fracturing fluids, demonstrating increased resistance to temperature thinning and physical shear, have also been prepared using reticulated bacterial cellulose, a gellant and a crosslinking agent, U.S. Pat. No. 5,350,528.
Methods of drilling formations, using aqueous well bore drilling muds containing reticulated bacterial cellulose, are disclosed in U.S. Pat. No. 5,362,713. The drilling muds additionally may contain water soluble polymers, such as cellulose derivatives, polyacrylamides or other polysaccharides.
Morano, U.S. Pat. No. 5,366,750, discloses edible non-aqueous thermostable compositions, containing ultrahigh surface cellulose materials, such as bacterial fermentation cellulose, that are pre-dried with a chaotropic agent, preferably corn syrup, for use as food product fillings or cremes. These compositions have an ultra-low water activity and additionally contain an edible non-aqueous hydrophilic liquid.
However, there still exists a strong need for versatile and stable rheologically modified polyol compositions useful for industrial applications. These highly desirable compositions would possess good flow properties, permitting pumping and pouring, and would enhance the value of current polyol applications.